How to use the relativistic doppler shift calculator
Find the observed wavelength of light from a fast-moving source moving towards or away from you. Enter emitted wavelength, source speed as fraction of light speed in the fields above; the observed wavelength if approaching, observed wavelength if receding are computed instantly and plotted on the chart so you can see how the answer changes.
Common searches this calculator answers include “relativistic doppler”, “redshift from moving source”, “approaching light wavelength”, “calculate relativistic doppler shift”, “find observed wavelength if approaching”.
Formula
Variables
- lam0 — Emitted wavelength (nm)
- beta — Source speed as fraction of light speed
Worked example
With emitted wavelength = 656 nm, source speed as fraction of light speed = 0.1, the calculator gives observed wavelength if approaching ≈ 593.3743 nm; observed wavelength if receding ≈ 725.2353 nm.
Frequently asked questions
What is the relativistic doppler shift calculator used for?
Find the observed wavelength of light from a fast-moving source moving towards or away from you. It helps with questions such as “relativistic doppler”, “redshift from moving source”, “approaching light wavelength”.
What is the formula for the relativistic doppler shift calculation?
Observed wavelength if approaching (nm) = lam0 × √((1-beta) / (1+beta)). Observed wavelength if receding (nm) = lam0 × √((1+beta) / (1-beta)). Here lam0 is emitted wavelength (nm), beta is source speed as fraction of light speed.
What inputs do I need for the relativistic doppler shift calculator?
You need emitted wavelength in nm, source speed as fraction of light speed. Each field is pre-filled with a typical example so you can see how the result responds as you edit the numbers.
How do I use the relativistic doppler shift calculator?
Type values into the input fields. Results and the chart update instantly. Use Reset to restore the example values, Copy results to paste them elsewhere, or Share to copy a link that preserves your inputs.
Is the relativistic doppler shift result exact?
Calculations use standard formulas and double-precision arithmetic, then display about seven significant figures. Real-world measurements carry uncertainty, so treat results as estimates unless your inputs are exact.